Tunable naturally-derived oligomeric ionic liquids: phase behavior and liquid crystal profile

Ionic liquid crystals (ILCs) derived from functional compounds obtained from natural sources, such as fatty acids (FAs), are promising compounds due to their sustainable appeal, low cost, and nutritional value. To expand the application of naturally-derived ILCs, this work discloses the use of the oligomeric approach to tune the LC and melting profiles of ILCs derived from FAs (stearic and oleic acids) and choline by mixing them to their parent FA. The oligomeric systems were investigated through the characterization of the solid-{[}liquid crystal]-liquid (S-LC-L) thermodynamic equilibrium. S-LC transitions were modelled using Margules and Margules-UNIFAC approaches, with the former presenting better results. The systems presented melting profiles similar to eutectic mixtures with a nonideal behavior and formation of solid solutions. The reduction of the melting point and the LC temperature window was related to the concentration and presence of unsaturation in the molecular structure of the components. The LC mesophases were formed at a wide temperature and FA concentration range. Oleic acid-based system presented lower melting points and a broader LC temperature domain with possibly two types of mesophases (lamellar and inverted hexagonal). Therefore, the oligomeric approach promoted the tunability of the LC and melting profiles of naturally-derived ILCs, which might expand their industrial applicability as lubricants, solvents and reaction media for low or high temperature processes, or as structuring agents (e.g. melting profile modifier) for the design of natural-based products. (C) 2021 Elsevier B.V. All rights reserved. (AU)